perf stat: No need to setup affinities when starting a workload

I.e. the simple:

  $ perf stat sleep 1

Uses a dummy CPU map and thus there is no need to setup/cleanup
affinities to avoid IPIs, etc.

With this we're down to a sched_getaffinity() call, in the libnuma
initialization, that probably can be removed in a followup patch.

Acked-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20220117160931.1191712-3-acme@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index 973ade18b72a947900405d676c92b11135946525..934e992c966fb950984a07dca737e9af861758f9 100644 (file)
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -788,7 +788,7 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx)
        const bool forks = (argc > 0);
        bool is_pipe = STAT_RECORD ? perf_stat.data.is_pipe : false;
        struct evlist_cpu_iterator evlist_cpu_itr;
-       struct affinity affinity;
+       struct affinity saved_affinity, *affinity = NULL;
        int err;
        bool second_pass = false;
 
@@ -803,8 +803,11 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx)
        if (group)
                evlist__set_leader(evsel_list);
 
-       if (affinity__setup(&affinity) < 0)
-               return -1;
+       if (!cpu_map__is_dummy(evsel_list->core.cpus)) {
+               if (affinity__setup(&saved_affinity) < 0)
+                       return -1;
+               affinity = &saved_affinity;
+       }
 
        evlist__for_each_entry(evsel_list, counter) {
                if (bpf_counter__load(counter, &target))
@@ -813,7 +816,7 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx)
                        all_counters_use_bpf = false;
        }
 
-       evlist__for_each_cpu(evlist_cpu_itr, evsel_list, &affinity) {
+       evlist__for_each_cpu(evlist_cpu_itr, evsel_list, affinity) {
                counter = evlist_cpu_itr.evsel;
 
                /*
@@ -869,7 +872,7 @@ try_again:
                 */
 
                /* First close errored or weak retry */
-               evlist__for_each_cpu(evlist_cpu_itr, evsel_list, &affinity) {
+               evlist__for_each_cpu(evlist_cpu_itr, evsel_list, affinity) {
                        counter = evlist_cpu_itr.evsel;
 
                        if (!counter->reset_group && !counter->errored)
@@ -878,7 +881,7 @@ try_again:
                        perf_evsel__close_cpu(&counter->core, evlist_cpu_itr.cpu_map_idx);
                }
                /* Now reopen weak */
-               evlist__for_each_cpu(evlist_cpu_itr, evsel_list, &affinity) {
+               evlist__for_each_cpu(evlist_cpu_itr, evsel_list, affinity) {
                        counter = evlist_cpu_itr.evsel;
 
                        if (!counter->reset_group && !counter->errored)
@@ -904,7 +907,7 @@ try_again_reset:
                        counter->supported = true;
                }
        }
-       affinity__cleanup(&affinity);
+       affinity__cleanup(affinity);
 
        evlist__for_each_entry(evsel_list, counter) {
                if (!counter->supported) {